The Gordon Research Conferences bring together the most active researchers in a given area of research for the purpose of in-depth discussion, including the exchange of new and unpublished ideas and technology, that will strengthen research efforts in the field. The 1990 Conference on Hormone Action represents the 21st conference in the series. The conference will continue to provide a forum for the latest advances in molecular and cellular endocrinology. Sessions on hormonal regulation of gene expression will focus on steroid hormones as general models for hormonal control of transcription, and on recent exciting advances in our understanding of the signal transduction pathways employed by other classes of hormones. Related sessions will deal with hormone action in lower eukaryotes (yeast), and with hormonal regulation of development. Recent advances in cellular endocrinology will be covered in sessions on hormonal regulation of secretion, transmembrane signalling in normal and neoplastic cells, growth factors and oncogenes, and hormones and reproductive function. This conference brings together an unusually diverse group of individuals ranging from basic scientists studying molecular mechanisms of hormone regulation, to physiologists and physician scientists interested in the integrative actions of hormones and their application to human disease. The limited attendance policy coupled with highly successful poster sessions, in which both younger scientists and senior investigators present their unpublished work, fosters the exchange of ideas. The Gordon Conference Foundation generously supports these conferences, but cannot provide sufficient funds to cover most major expenses of speakers. Solicitation of private funds is not permitted. Therefore sources of support such as the National Institutes of Health are critical to the continuing success of the conference.